A method for ion phase space validation for below therapeutic ion fluences (by single ion tracking)
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2018
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Abstract
A wide-spreading technique for treating cancer patients in developed countries is ion beam radiation therapy. This is due to the advantageous dose deposition pattern of ions and to their radiobiological effects in tissue.The dose calculation procedure for the treatment planning of this kind of therapy requires a facility-specific ion beam model. A phase space of the particles leaving the beamline represents an alternative to the simulation of the complete beamline. In experiments with the silicon pixelated detector TimePix, 2-3 orders of magnitude of lower fluences than therapeutic ones are required, so the detector is not saturated. A method for assessing the validity of the therapeutic phase spaces under low fluence operation was developed in this thesis. The investigation included proton, helium, and carbon ion beams, using a phantom-free tracking system. This system was composed of two TimePix detectors. Measured and simulated primary ion track distributions were compared based on the width of their angular distributions. In general, wider angular distributions were obtained for the measured primary tracks than in the Monte Carlo simulations with pregenerated phase space files considering a continuous detector. The narrower the beam, the larger the obtained differences between measured and simulated width of the angular distributions. Above the limit of the angular resolution of the tracker (0.84*), the measured difference to Monte Carlo calculations was above 2.1%. In the future, an improved angular resolution of the tracking system and an improved alignment procedure are needed to make a final statement about the accuracy of the phase space files in the low fluence range for the whole span of available beam widths. This work establishes a methodology for a track-based comparison between Monte Carlo simulations and measurements using single-ion tracking.
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Tesis (Master in Clinical Medical Physics)--Pontificia Universidad Católica de Chile, 2018